In a modern society, transportation devices such as automobiles having a combustion engine are inevitable. As a fuel pump of the automobile or the like, a lot of electromagnetic driving fuel pumps that incorporates a motor portion and a pump portion are used.
A principle of the electromagnetic driving fuel pump is as follows. When a contact portion of a commutator of the motor portion comes into contact with a brush, an electric current is supplied from a power source to an armature to rotate the armature. When the armature is rotated, an impeller of the pump portion is rotated to pump fuel from a fuel tank to supply it to an engine.
In general, a commutator that is used in a fuel pump like this is in many cases made of copper.
However, there is a problem in that, since a copper commutator is oxidized or exposed to gasoline or the like containing sulfur or an alcoholic component, the commutator per se is likely to be corroded.
In this connection, in recent years, in place of the copper commutator, carbon commutators shown in patent literatures 1 through 3 below are proposed.
Patent literature 1: JP-A-8-126259
Patent literature 2: JP-A-8-308183
Patent literature 3: JP-A-10-162923